Yes, it was converted from flint. The round drum, and filled holes in the lock plate give it away.
It is an example of a common trade quality pistol. The brass barrel is a nice feature, and found on the slightly better quality guns, but this is still an export/trade pistol. Most likely made in Birmingham, or possibly in Belgium. There should be proof marks somewhere, maybe on the underside of the barrel?
If there are no proof marks it is possible it could have been assembled in America from purchased surplus parts. The parts and style are too generic to pinpoint any particular place of origin. Unfortunately, the word "London" stamped on the lock is meaningless.
And oh yeah, there is a good chance it is still loaded.